1. FIELD OF THE INVENTION
The invention relates to the construction of an inflatable packing element for use in inflatable packers or bridge plugs employed in subterranean wells.
2. SUMMARY OF THE PRIOR ART
Inflatable packers (or bridge plugs) have long been utilized in subterranean wells. Such inflatable tools normally comprise an elastomeric sleeve element mounted in surrounding relationship to a tubular body portion. Pressured fluid is communicated from the surface of the well to the bore of the tubular body and then through radial passages to the interior of the elastomeric sleeve. To protect the elastomeric sleeve, it is customary to completely surround the elastomeric sleeve with a plurality of peripherally overlapping, resilient, reinforcing slats or ribs. The medial portions of the reinforcing ribs are surrounded and may be bonded to an outer annular elastomeric packing element or cover of substantial wall thickness. Upper and lower securing assemblies respectively engage the ends of the elastomeric sleeve and the reinforcing ribs and is fixedly and sealably secured relative to a central tubular body. A lower securing assembly is secured to a sealing sub which is mounted for slidable and sealable movement on the exterior of the central tubular body, in response to the inflation forces. A structure of this general type is shown in U.S. Pat. No. 3,160,211 to MALONE.
With inflatable packers of this type, very substantial tensile forces are exerted on the reinforcing slats or ribs during the inflation of the elastomeric sleeve. It has been customary to clamp the ends of the ribs to the upper and lower securing assemblies, but such clamping arrangements are subject to failure if the inflatable packer is repeatedly inflated for engagement with different portions of the well casing or conduit in which it is inserted.
More recently, the ends of the flexible ribs have been welded to an internal surface of a securing sleeve, in the manner indicated in FIG. 1 of the drawings. If the welding operation is properly accomplished, this provides a secure anchoring of the ends of the flexible ribs to the mounting sleeve, but those skilled in the art will recognize the difficulty of making consistently good welds within the relatively small bore of a mounting sleeve for the inflatable packing element of an inflatable packer. If one or more of the ribs is not properly welded, such ribs will break loose under the tensile forces imposed by the inflation of the elastomeric sleeve packer or element which is inserted within the ribs and, because there is thus created a weak area in the cylindrical cage of the reinforcing ribs, the substantial fluid pressure applied to the inflatable elastomeric sleeve can well push such rib out of alignment with the other ribs and thus produce a potential area of breakage of the inflatable elastomeric sleeve because it will follow the outward displacement of the unanchored rib and form a thin walled bubble.
There is a need therefore for an anchoring system for the peripherally stacked cage of flexible reinforcing ribs which normally surround the inflatable elastomeric sleeve of an inflatable packer or bridge plug which effects a reliable rigid connection of the ends of the ribs to the mounting sleeves for the expansible packing element.